The present invention relates generally to sealing devices for valves, particularly high pressure and high temperature seals for valves having a pivotal closure member, such as butterfly or ball valves. More specifically, the present invention relates to valve sealing devices having high temperature destructible and undestructible seals.
Valves for use in systems transporting combustible fluids, such as petroleum or other hydrocarbons, or in systems where fluids are transported through inflammable environments, must provide effective sealing at normal temperatures and pressures as well as at elevated temperatures and pressures, resulting because of a fire in the vicinity of the transport system, in order to prevent fluid leakage. Prior art devices, such as that disclosed in U.S. Pat. No. 3,734,457, to Roos, have employed high pressure and temperature resistant materials, such as "Teflon" in valve seats, but these materials are not suited for sustained sealing at fire temperatures (over 750.degree. F.). Prior art devices have also employed sealing devices containing metallic sealing rings, for use at fire temperatures and pressures, in combination with heat destructible resinous, polymeric, or elastomeric sealing rings, for use at lower or moderate temperatures and pressures (often only up to 250.degree.0 F. and 300 psi). While these dual seal devices have generally performed satisfactorily, they are often very costly and difficult to assemble or replace due to the unique component configurations employed. Also, when a fire destroys the low temperature sealing ring, debris from that ring sometimes flows through the valve or remains in the vicinity of the high temperature sealing ring in such a way as to interfere with the proper sealing of the remaining sealing ring and, thus, creates leakages of fluid which may cause the fire to spread.
Similar problems have been encountered in providing effective valve seals for fluids transported through, or themselves maintained at, high temperatures (approximately 1000.degree. F.). Prior art devices have usually consisted of metal sealing rings which may be spring or pressure biased against the movable valve member. Again, these sealing devices have usually been costly to produce and difficult to install in the valve. Less expensive devices typically are incapable of effective sustained operation at high temperatures as they may become unseated and/or deformed.